From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [RFC PATCH 0/2] irq destination caching prototype Date: Mon, 13 Aug 2012 14:12:41 +0300 Message-ID: <20120813111241.GY3341@redhat.com> References: <5028CAA9.8070807@redhat.com> <20120813101246.GA16147@redhat.com> <20120813101608.GS3341@redhat.com> <5028D52D.9050104@redhat.com> <20120813102402.GT3341@redhat.com> <5028D788.3070006@redhat.com> <20120813103845.GA16300@redhat.com> <5028DDCD.1090205@redhat.com> <20120813110108.GX3341@redhat.com> <5028DF17.2050008@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Michael S. Tsirkin" , kvm@vger.kernel.org, Jan Kiszka To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:16071 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751006Ab2HMLMq (ORCPT ); Mon, 13 Aug 2012 07:12:46 -0400 Content-Disposition: inline In-Reply-To: <5028DF17.2050008@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Mon, Aug 13, 2012 at 02:03:51PM +0300, Avi Kivity wrote: > On 08/13/2012 02:01 PM, Gleb Natapov wrote: > >> > >> Actually this is overkill. Suppose we do an apicid->vcpu translation > >> cache? Then we retain O(1) behaviour, no need for a huge cache. > >> > > Not sure I follow. > > Unicast MSIs and IPIs can be speeded up by looking up the vcpu using the > apic id, using a static lookup table (only changed when the guest > updates apicid or a vcpu is inserted). > To check that MSI/IPI is unicast you need to check a lot of things: delivery mode, shorthand, dest mode, vector. In short everything but level. This is exactly what kvm_irq_delivery_to_apic() is doing. Caching apicid->vcpu is not enough, caching (delivery mode, shorthand, dest mode, vector)->vcpu is enough and this is exactly what the patch does for irq routing entries. -- Gleb.